1. Field of the Invention
This invention relates to the field of self-propelled, center-pivot irrigation systems in which a radially extending distribution pipe moves about a central location to apply water over a circular area or a segment of a circular area.
2. Description of the Prior Art
Self-propelled, center-pivot irrigation systems generally comprise a centrally located pivot assembly with an overhead distribution pipe extending horizontally therefrom. The distribution pipe is supported and propelled about the central pivot assembly by a plurality of towers spaced along its length. Each tower has its own drive arrangement which is commonly powered by hydraulic fluid or electricity flowing in lines that extend outwardly from the central pivot assembly. In some systems, the hydraulic or electric lines are merely extended from a source at the central pivot assembly out to the drive motors. With such systems, a problem develops in that the lines will become wrapped around the central pivot assembly upon repeated revolutions of the distribution pipe. An example of such a system is U.S. Pat. No. 3,648,930 Brown et al. issued on Mar. 14, 1972 in which the electric cable extends from an electrical source at the central pivot assembly out to the drive motors for each tower. To avoid having to monitor such systems and periodically unwrap the lines, some arrangements like U.S. Pat. No. 3,784,106 to Ross issued on Jan. 8, 1974 extend the lines upwardly through the center pivot pipe; however, this creates additional problems with maintenance and restricts the flow of water through the pipe.
Several designs for electrically powered irrigation systems have been patented as for examples U.S. Pat. No. 3,659,627 to Zimmerer et al. issued on May 2, 1972, U.S. Pat. No. 3,750,953 to Reinke issued on Aug. 7, 1973, and U.S. Pat. No. 3,782,408 to Martin issued on Jan. 1, 1974. Each of these patented designs enables electricity to be passed from a stationary source to a rotating pipe without restricting the water flow through the pipe and without having any lines wrap around the assembly as the pipe rotates. Hydraulic designs for accomplishing essentially the same result are best illustrated by U.S. Pat. No. 2,781,134 to Weir et al. issued on Feb. 12, 1957 (see his FIGS. 4 and 7) and U.S. Pat. No. 2,701,146 to Warren issued on Feb. 1, 1955.
Self-propelled, center-pivot irrigation systems have one particular problem that has not been satisfactorily overcome to date. This problem occurs when the land to be irrigated is not absolutely flat and involves the torque forces applied to the central pivot assembly as the distribution pipe is moved over the uneven land. Rigid assemblies like Zimmerer, Reinke, Martin, Weir, and Warren cannot adjust to the up and down movement of a distribution pipe with the result that a destructive amount of force can be applied to the central pivot assembly. Such force is particularly harmful to the central pivot assembly of irrigation systems powered by hydraulic fluid because it can separate, weaken, and break the seals between members causing a loss of hydraulic pressure and fluid. Since reliability and durability are key factors in the success of any irrigation system, any breakdowns caused by these forces are directly reflected in lost sales and profits. Ball joint assemblies such as U.S. Pat. No. 3,957,291 to Edling et al. issued on May 18, 1976 which permit limited universal movement are available; however, none will reliably and satisfactorily perform the multiple functions of permitting water to flow from a stationary pipe to a rotating, pivoting pipe while simultaneously permitting hydraulic fluid to flow continuously along separate out and return paths between a stationary source and the same rotating, pivoting pipe. The assembly of the present invention is designed to perform these multiple functions in a reliable and durable manner.